Target-seeking head for guided missile



Aug. 22, 1961 D. s. CARY ETAL TARGET-SEEKING HEAD FOR GUIDED MISSILEFiled March 19, 1958 L w Ev W e a m 556% x a mm m 528 G K M m 56m 5.86sis E \v v E m d n n EsE f mm m I NEmE E w. an o o w! t EH2 wv ("v D RSBY ,2? .Q d

Wd' ATTORNEYS United s tates Patent F 2,997,595. TARGET-SEEKING HEAD FORGUIDED MISSILE Donald S. Cary and Robert E. Kesel, Rochester, N.Y.,

and Stephen M. MacNeille, Thompson, Conn., assignors, by mesneassignments, to the United States of America as represented by theSecretary of the Navy Filed Mar. 19, 1958, Ser. No. 722,621

2 Claims. (Cl. 250-203) This invention relates to a target-seeking headfor guided missiles which is particularly Well adapted for generatingguidance signals derived from infrared or other radiant energy emanatingfrom a target whereby to direct the missile into a collision course withthe target. Like many guidance systems for this same general purpose, itis a two coordinate system utilizing a separate set of target-sensingelements for each of two rectangularly related coordinate planes which,for ease of description will be termed the left-right and up-downplanes.

It is well known in the art that so long as the line of sight from amissile to a given target remains at a constant angle with the axis ofmotion of the missile, the latter will be on a true collision coursewith the target. On the other hand any shift in the angle of the line ofsight indicates that the missile is off course in one direction oranother, the direction and rate of shift of the sighting angle beingindicative of the corrective control action necessary to bring themissile back into its desired collision course.

It is therefore an object of this invention to provide a target-seekinghead for sensing the direction and extent of shift in the line of sightfrom a missile to a target and which is capable of producing outputsignals, useable for control purposes, indicative of this shift.

It is a further object of this invention to provide such atarget-seeking head wherein a scanning element is caused to sweep at aconstant linear rate across animage of the target field, the scanningelement being arranged to alternately interrupt and then pass radiantenergy emanating from the target.

It is a further object of this invention to provide such atarget-seeking head wherein, for each coordinate plane, means areprovided for directing energy emanating from said target along twosimilar but separate paths onto separate detectors, and wherein amodulating scanner is caused to sweep across both of said paths at aconstant linear rate, the energy in each of said paths being broughtinto focus at the plane of said scanner to form a pair of target imagesso spaced relative to one another that the energy striking the detectorswill be modulated at a frequency indicative of the dynamic relationshipof the line of sight to the missile axis and the modulations at thedetectors will be 180 out of phase with one another, the detectors beingso connected together that each serves as a load for the other duringalternate half cycles whereby the combined output signals derivedtherefrom will be of substantially twice the peak-to-peak amplitudeobtainable from a single detector under similar conditions.

Further objects of the invention will become apparent from the followingdescription and claims were considered in the light of the accompanyingdrawing wherein:

FIG. 1 is a front view of a missile incorporating our invention, partsbeing broken away better to show the internal construction;

FIG. 2 is a fragmentary longitudinal sectional view through the forwardportion of the missile;

FIG. 3 is a partially diagrammaitc representation of a portion of theoptical system used in our invention; and FIG. 4 is a block diagram of asystem which may be uti1izd with our invention for converting theinforma- 2,997,595 Patented Aug. 22, 1961 tion derived from thetarget-seeking head to a form useable for control of the missile.

Our invention is shown as being applied to a missile 1 which may beprovided with a pair of bulkheads 2 and 3 in the forward portionthereof. The missile is provided with a nose unit 4 formed of a suitablematerial which is transparent to the particular type of radiant energywhich is to be utilized for guidance. Mounted in a pair of openings 5and 6 in the bulkhead 2 are a pair of objective lenses 7 and 8 whichwill be described in more detail herebelow. Carried by a rotary drivenshaft 9 journalled in suitable bearings 10 in bulkhead 3 in a scanningdrum 11, the periphery of which is in the form of a portion of a sphere.The inner surface 12 of this scanning drum is coated with an energyreflecting material so as to produce a series of alternately arrangedreflecting strips 13 separated by non-reflecting portions 14. Shaft 9 isadapted to be driven at a constant speed, as by a suitable motor 9,which, with the shaft, constitutes means for rotating the scanning drum11 at a constant angular rate. Mounted axially rearwardly of theobjective lenses 7 and 8 as by a suitable bracket structure 15, are apair of plane mirrors 16 and 17, so oriented as to reflect rays ofenergy passing through the lenses 7 and 8 onto the inner surface 12 ofthe scanning drum 11. The focal lengths of lenses 7 and 8 are such thatrays emanating from a distant object will be brought into substantialfocus at the inner surface 12 of the drum, those rays impinging at anyparticular instant upon a strip of reflecting material 13 beingredirected thereby toward one of the two collecting lenses 18 or 19, tothe rear faces of which are secured energy sensitive detectors 20 and21, respectively.

As best shown in FIG. 3 the rear surfaces of the lenses 7 and 8 arepainted or coated as shown at 22 so as to provide four elongatedentrance pupils or apertures 23-26. Each of the detectors 20-21 alsocomprises four detector elements 2'7-30 of similar shape, the collectorlenses being so designed in conjunction with the remainder of theoptical system that they eifectively image the entrance pupilsindividually onto the corresponding detector elements. Thus, with thisarrangement, rays passing through aperture 23 of lens 7 and which arereflected by the drum 11 onto collector lens 18 will impinge upondetector element 27, while those passing through aperture 26 willsimilarly impinge upon detector element 30, etc.

Each of the objective lenses 7, 8 is likewise provided on its rearsurface with a wedge prism 31 which covers two of the apertures 25 and26 and is arranged to deflect the bundles of rays 34 and 35 passingtherethrough so that they will he focused on the drum surface 12 at apoint spaced one half of the pitch distance between adjacent reflectingstrips 13 from the point at which bundles of rays 32-33 emanating fromthe same source and passing through apertures 23 and 24 will impingeupon said drum surface. By pitch distance is meant the angular distancealong the periphery of the drum between corresponding points on any twoadjacent strips 13. Thus, at any particular instant, the bundles of rays32-33 passing through apertures 2324 will fall on a reflecting strip 13as indicated in FIG. 3 while at this sarne instant, the rays 34-35 fromthe same source and passing through apertures 2526 will impinge upon theadjacent nonreflecting strip 14 of the drum. Thus, at this instant, thebundles of rays 32 and 33 will be reflected by the strip 13 onto thecorresponding detectors 2728 'while the rays 3435 will not be reflectedand the corresponding detectors 29-30 will be unillurninated. However,an instant later, when the drum has rotated an amount corresponding toone-half the spacing between adjacent reflecting strips '13, rays 34 and35 will be reflected onto the corresponding detectors 29 and 30 whiledetectors 27 and 28 will be unilluminated. Thus, the two pairs ofdetector elements making up each of the detectors 2021 will bealternately illuminated at a frequency depending upon the rate ofrevolution of the scanning drum 11 and the number of sets of reflectingand nonreflecting strips 13 and '14. Where the line of sight to thetarget from the missile remains at a fixed angle relative to thelongitudinal axis of the missile, the images of the target will remainat *fixed points on the periphery of the drum 1 1 and the resultingoutput pulses from the detectors 20 and 21 will therefore occur at apredetermined frequency Which will hereinafter be termed the normalscanning frequency. However, if the line of sight to the target isshifting relative to the longitudinal axis of the missile the images ofthe target will likewise be shifting. Any component of movement of theseimages which is parallel to the peripheral movement of the drum "at thatparticular location will result in either an increase or decrease, asthe case may be, in the frequency of the output "signals from thedetectors 20 or 21. Therefore, by comparing the frequency of the signalsoccurring at the outputs of these detectors with the normal scanningfrequency 'a signal indicative of the relative direction and rate ofshift of the line of sight relative to the missile axis may be obtainedwhich may be utilized to initiate appropriate control corrections.

While many different arrangements could obviously be utilized 'forobtaining such correction signals a system such as is described andclaimed in the copending application of Edward 0. Dixon and Stephen M.MacNeille, Serial No. 722,620, field concurrently herewith, isparticularly well adapted for this purpose.

To facilitate the conversion of the output from the detectors 20, 21into such useable control signals, a commutator 36 may be mounted onshaft 9 for rotation therewith, the commutator being provided withalternately arranged conducting and insulating segments 38 correspondingin number to the number of reflecting and nonrefiecting strips 13 and 14on the drum 11. Suitable brushes, diagrammatically indicated at 39-42,contacting the periphery of the commutator may serve as sources of thenormal scanning frequency useable for such signal.

conversion. Thus, as is diagrammatically indicated in FIG. 4, the outputof detector 20 is applied to a leftright discriminator 43 controlled bycommutator brushes 39 and 40 while the output from detector 21 is fed toa similar up-down discriminator 44 controlled by the brushes 41, 42. Fora detailed description of these discriminators reference should be madeto the above-mentioned copending application Serial No. 722,620. Sufiiceit to say that each of these discriminators is so arranged as to produceat its output 45 or 46 a control signal indicative of both the relativedirection and extent of difference between the associated detectoroutput and the normal scanning frequency. This output may there fore bedirectly utilized to control both the direction and degree of correctivecontrol action to be taken.

As is also indicated diagrammatically in FIG. 4 the pairs of detectorelements 27 28 and 2930 which "be obtained with a single detector orpair of detectors and a conventional load resistor. The individualdetectors 2728 and 29-30 of each pair may be connected either inparallel with one another as indicated in FIG.

4 or in series depending upon the impedance of the detector-input stageof the associated discriminator.

"Operation of the invention is believed to have been 'maue obvious fromthe preceding description. Ra s of energy from a target passing throughthe apertures 23-26 of the objectives 7 or 8 will be alternatelyreflected by the reflecting strips 13 of the scanning drum 11 onto thecorresponding detector elements 27-30. The resulting pulsating outputsfrom these detectors will be applied to the corresponding discriminator,compared with the nor mal scanning frequency derived from the commutatorbrushes and converted into a form suitable for corrective controlpurposes.

From the above description it is believed apparent that we havedisclosed a target-seeking scanning head for a missile which is ofrelatively simple construction and which is well adapted to the desiredpurpose. Obviously, the materials utilized in the optical components ofthe system will depend upon the particular type of radiant energy whichis to be detected by the head and materials suitable for light orinfrared or other types of radiation are well known to those skilled inthe art. Obviously, many variations in the specific arrangement of theparts as disclosed herein may be made without departing from theprinciples of the invention. While we have shown four apertures and fourdetector elements associated with the scanning system for eachcoordinate plane, the number of such elements may obviously be variedwithout departing from the general mode scribed in the companionapplication of Dixon and Mac- Neille Serial No. 722,620 it will beequally obvious to those skilled in the art that other types ofdiscriminators may be substituted without invention and that many otherchanges may be made without departing from the spirit and scope of theinvention as defined by the ap pended claims.

In the specific embodiment disclosed, to avoid unnecessary confusion,the line of flight of the missile has been "assumed to be coincidentwith the longitudinal axis of the missile and the seeker head hastherefore been shown as rigidly mounted on the missile. As is well knownin the art, in an actual missile the seeker head would normally becarried on a gyro stabilized assembly within the missile so that pitchor' yaw motions of the missile would not produce false guidanceinformation. The principles of the invention are obviously equallyapplicable to such an arrangement and the term missile axis as usedherein is intended to mean the actual line of flight of the missilewhether it be coincident with the longitudinal axis of the missileitself or to a gyro-stabilized reference axis within the missile.

We claim:

1. A target seeking head for generating signals indicative of thedynamic relationship, in a given coordinate plane, of the line of sightfrom the head to a target to a predetermined reference axis through saidhead, comprising a pair of energy responsive detectors, means forming apair of apertures, and means for directing energy emanating from saidtarget and passing through said "te'ct'ors, said energy directing meansincluding energy focusing means in each path arranged to form an imageof said targets; the point in each path Which iS traversed by saidmodulating elements of said scanning means, said images being spacedlaterally from one another in the direction of movement of saidmodulating elements a distance equal to an odd multiple of one half thepitch distance between successive modulating elements, said energydirecting means being so arranged relative to said scanning means thatany shifting of said line of sight relative to said reference axis insaid coordinate plane will produce a corresponding shifting of both ofsaid target images in the same direction along the path of movement ofsaid modulating elements whereby the modulations of the energy reachingsaid detectors will be 180 out of phase and at a frequency indicative ofthe dynamic relationship of said line of sight to said reference axis insaid coordinate plane.

2. A target seeking head as in claim 1 wherein said energy directingmeans includes an objective lens common to both paths for forming saidimages and wherein a wedge prism is positioned adjacent one of saidapertures to relatively deflect the energy passing through said lens andsaid one aperture whereby to produce the desired 10 separation of saidimages.

No references cited.

